Thrombosis

What is factor V Leiden?

The most common genetic risk factor for venous thrombosis is factor V Leiden, present in 5 percent of the general population. Factor V is one of the normal blood clotting factors. Factor V Leiden is a changed or "mutated" form of factor V that is inactivated 10 times slower than the normal factor V. This causes it to persist longer in the circulation, resulting in a hypercoagulable state. In other words, the blood continues clotting, resulting in possible obstruction.

One copy of the factor V Leiden gene increases the risk for venous thrombosis 4 to 8 times, while two copies of the gene increase the risk 80-fold.

Other coexisting coagulation defects can occur with factor V Leiden, and in general, the risk for thrombosis increases in patients with more than one genetic defect.

The factor V Leiden mutation is involved in 20 to 40 percent of venous thrombosis cases and is suspected in individuals who have a medical history of venous thrombosis or in families with a high incidence of venous thrombosis.

What is thrombosis?

Thrombosis occurs when clots obstruct or block veins (blood vessels that carry blood from the body back into the heart) or arteries (blood vessels that carry oxygenated blood away from the heart to the body). Venous thrombosis is when the blood clot obstructs a vein, and arterial thrombosis is when the blood clot obstructs an artery.

What causes thrombosis?

Venous thrombosis may be the result of the following:

Disease or injury to the veins in the legs

Immobility for any reason

Fracture

Certain medications

Obesity

Inherited disorders or inherited predisposition

Autoimmune disorders that predispose to clotting

Medications, such as certain contraceptives, that increase the risk of clotting

Pooling (stasis) of blood in the legs and subsequent clotting can result in varicose veins. Clots in the legs may break loose and travel to the lungs, causing pulmonary clots that can result in respiratory distress, pain, and in extreme cases, death.

Arterial thrombosis may be the result of arteriosclerosis, which involves hardening of the arteries where fatty or calcium deposits cause the arterial walls to thicken. This can lead to plaque instability and risk for rupture followed by thrombus.

When arterial thrombosis occurs in the coronary arteries (arteries that branch from the aorta to provide blood to the heart muscle), it can lead to heart attacks. When arterial thrombosis occurs in the cerebral (brain) circulation, it can lead to strokes or lack of oxygen to other organs.

Risk factors for arterial thrombosis may include:

Smoking

Diabetes

High blood pressure

High cholesterol

Lack of activity and obesity

Poor diet

Family history of arterial thrombosis

What are the symptoms of thrombosis?

The following are the most common symptoms of thrombosis. However, each individual may experience symptoms differently. Symptoms may include:

Pain isolated to one leg (usually the calf or inner thigh)

Swelling in the extremity

Chest pain

Numbness or weakness on one side of the body

Acute mental status changes

The symptoms of thrombosis may resemble other blood disorders or medical problems. Always consult your doctor for a diagnosis.

How is thrombosis diagnosed?

In addition to a complete medical history and physical examination, diagnostic procedures for thrombosis may include venous and arterial ultrasounds and blood tests including hypercoagulability panels. Dye injection with angiography and catheterization may also be used, as well as MRI/MRA and CT. The diagnostic procedure advised depends on the type of thrombus--venous or arterial--and the location

Treatment for thrombosis

Specific treatment for thrombosis will be determined by your doctor based on: